944 Turbo engine trouble..

Shark · Sep 4, 2014

Hi folks,

I got my 951 a few weeks ago, though I am not new to the model, I have had a few 951's in the past..

It's a 1990 250 car.

This car was running fine, then out of the blue the power cut whilst driving - for only 1 second - a little blip.. then it was running fine again for a few miles. the fuel was low so I fuelled up. All was well for another couple miles, then all of a sudden it lost power again and coasted to a halt. It would not start.
I waited a few mins then turned it over again, it started and was running perfectly for another 25 motorway miles.
When I arrived home with it, it cut out again at the end of the road. I tried to start it and managed to get it to run but it would not idle and was running on what felt like two cylinders, I can manage to ease the revs up beyond 4500+ and the it evens out and runs smooth, but come off the gas and its back to running like two cylinders and will cut off if I come off the pedal. This is how it stands now.. starts only if you squeeze the pedal, runs rough and will not idle.

I swapped out the DME relay with an S2 that I have here and it made no difference (and the S2 would run with the relay from this car) so obviously not that at fault. There is plenty fuel in the car too.

Not sure where to go from here. If I can sort it myself it would mean I don't have to get it recovered and taken to specialist..

Any ideas?? Strange, it was running really well, smooth and quiet, producing good power and boosting well..

Thanks for any suggestions!!

Frenchy · Sep 4, 2014

Check the distributor cap, mine was running silly fine ione minute then cutting out and refusing to run, i went way too deep suspecting and checing allsorts of things, turned out to be excessive wear on the contacts in the distributor cap, new cap and rotor arm along with plugs.........................swiss watch !

robwright · Sep 4, 2014

Start hy checking all the electrics first. Plug leads, coil and dizzy. Check fuel pressure regulator, damper and all vacuum hoses.

George Elliott · Sep 4, 2014

Sorry to hear of your trouble

All the Vac lines in place around the engine?

Elec Grounds / Earths good

Dizzy Cap good

Plugs & leads good (Check at night in the dark to see ant arcing from the leads / cap)

No one has been power washing under the bonnet

AFM can play up - google 944 AFM to see tests with a 9v battery (needs to come off to check)

Elec connections to main components are clean / dry / secure - AFM, Throttle Switch, Coil, F/W Sensors, Injectors

Flywheel sensors show correct resistances (per Clarks garage / google)

Finally, 1, be patient, 2, beware specialists

Good luck
George
944t

Shark · Sep 4, 2014

Thanks guys, some good advice and things to check!

chrisg · Sep 4, 2014

If you're able to replicate the running on 2 cylinders behaviour and it will run like that, you can pull the plug leads individually to confirm which cylinders / not it's running on.

I would suspect from your symptoms it's a plug or dizzy cap issue.

First step I would suggest is replace all 4 plugs followed by the dizzy cap and rotor arm.

If no joy after that likely to be plug leads

They may be fast and a Porsche but the 951 is still a dizzy engine and they do benefit from regular change of plugs cap and arm.

Yours

Chris

Eldavo · Sep 5, 2014

Power blip sounds like the over boost protection. If you were in 3rd/4th giving it full beans under load then it can briefly overboost leading to the protection kicking in and it feels like someone's put the brakes on. Happened to me a few times with a boost enhancer and on a cold day at full chat in 3rd.

robwright · Sep 5, 2014

ORIGINAL: Eldavo

Power blip sounds like the over boost protection. If you were in 3rd/4th giving it full beans under load then it can briefly overboost leading to the protection kicking in and it feels like someone's put the brakes on. Happened to me a few times with a boost enhancer and on a cold day at full chat in 3rd.

Too much boost? Does such a condition exist???? [

]

Shark · Sep 5, 2014

No, its not overboost, I know exactly what that feels like. Was just driving normally when it occurred. My thoughts are it has maybe been low on fuel and the gauge not being accurate (only had the car a few weeks so im unsure), it maybe picked up some dirt and blocked the fuel filter and or injectors. That's my feeling.. I will try a few of the above suggestions and report back.. thanks.

pengers · Sep 24, 2014

I had a long term cut-out problem with my '89 turbo.

I completely sympathise as it removes all confidence in reliability.

And any enjoyment. And it's v v difficult to demonstrate to a mechanic as it will undoubtedly run perfect on inspection.

Anyway, mine was crank shaft position sensor manifested in cut-out periods that lasted 5mins to 7hrs and eventually poor running on every start until warm.

Which at least was a reliable fault to diagnose.

Good luck, be prepared for a lengthy process

At least coil, leads, distributor cap, fueling system regulators and all the other small ancillary items that you may exchange in the process can ALL be viewed as consumables on a 25 yo motor and you will be buying reliability for the next 25 into the bargain..

So don't give up!

You will know your car well or at least much better by the time you've finished..

944 man · Sep 24, 2014

ORIGINAL: robwright

ORIGINAL: Eldavo

Power blip sounds like the over boost protection. If you were in 3rd/4th giving it full beans under load then it can briefly overboost leading to the protection kicking in and it feels like someone's put the brakes on. Happened to me a few times with a boost enhancer and on a cold day at full chat in 3rd.

Click to expand...

Too much boost? Does such a condition exist???? []

In theory, no. In practice though, Ive had the same issue with a boost enhancer.

George Elliott · Sep 24, 2014

When I arrived home with it, it cut out again at the end of the road. I tried to start it and managed to get it to run but it would not idle and was running on what felt like two cylinders, I can manage to ease the revs up beyond 4500+ and the it evens out and runs smooth, but come off the gas and its back to running like two cylinders and will cut off if I come off the pedal. This is how it stands now.. starts only if you squeeze the pedal, runs rough and will not idle.

Shark,
I'm reading this bit carefully........and it makes me think AFM. Here's why:

Your original problem occurred at around 2400rpm...? that and a bit below is he most worn area on the wiper in the unit. This area is the most used area. The wear has caused a bad voltage signal into the ECU, hence the hiccup.

The wiper position is determined by the flow of air into the engine, which is an outcome of the engine rpm.

Both of these are determined by throttle position.

You floor the pedal, the butterfly opens, allowing the suction / and eventually boost, to flow more air which forces the AFM flap further open and brings the wiper onto a new less worn are of the ceramic track, where the ECU gets good AFM info

I'm guessing you have to give it a Wide Open throttle to get out of the sub 2800 area...?

Hence the even running at 4500rpm, the wiper is sending good info to the ECU

Also, at startup, the AFM is ignored for a few seconds, so it will start, but then read the bad sector at 1400 to 2800 rpm and play up.

Hope you find it soon, I find its usually simple

Good luck
George
944t

Shark · Sep 24, 2014

Hi George, thanks for that post. It makes sense, I will relate the idea to the garage who have the car..

Listen to this (ok, lol...read this)..
I had to tow the car to the local garage. I wanted to take it to the nearest specialist but I would need a recovery wagon and would be £100 odd before I even got it there, so instead, we towed it a mile to the local..who is very good btw..

I took it there as arranged on Friday, flat battery and all (flattened due to trying to start it, testing, laying up unused etc). I gave them a visit today, the chap said all they had done was charge the battery, now waiting on a free ramp to get it up in the air to take a look at the starter more. I said WTF? nothing wrong with the starter..he explained he couldn't get it to turn over. I said I would show him how to start it..

We went over to the car..- now it has been 4 weeks since it ran properly- I jumped in, key in, ignition on, press the button on the fob then turn it over...

..bloody thing started and is running like a new Rolex. WTF?

Now, I have left it with them to try look for this "intermittent" fault. Which will be hard to find given it is running perfect. I would rather it had not started and was still not running right at least then that is a head start to chasing the fault!

What is your thoughts on that?

I will pass on your AFM theory.. Thank you for that!

George Elliott · Sep 25, 2014

Shark,

Intermittent electrical faults are a nightmare.....as you know

Perhaps a fully charged battery with maybe 0.8 added volts over a normal battery, so 6% additional voltage means the AFM track will be just above the threshold where it works?

Maybe a cold engine bay has less electrical resistance to a warm one (it has)

Maybe the copper wiper is shorter cold than hot, so it works better cold?

Maybe the copper wiper has greater spring tension cold than warm, so it works better

And if all these variables are combined, it runs like a Rolex.......for a while.

George
944t

Shark · Sep 25, 2014

Thanks George,

Perhaps a new AFM is required. An expensive item in the process of elimination though sadly.

Shark · Sep 25, 2014

Do the 951 and S2 share the same AFM? I could wait until it fails again then swap it over with my S2 and see if it replicates the same problem in the S2, and similar, see if the S2 AFM in the turbo solves the problem...

George Elliott · Sep 26, 2014

Others will confirm, but I think the S2 / turbo AFM is different ....

I think we still have a working turbo AFM spare but the enrichment adjusting screw is seized. It worked fine before being upgraded to Augtronic.

If you want it to try you are welcome, it has no value with the screw seized, but may help you eliminate this fault?

If you want it send me an address

George
944t

Shark · Sep 26, 2014

Thanks George,

I collected the car from the garage today, they couldn't find anything wrong with it, clean bill of health.
They tested the AFM as per the clarksgarage guide and it tested fine, its not the AFM causing the problem or at least it doesn't appear to be.

We both agreed it was uneconomical to spend hours looking for a fault, so I took it away and will wait for it to happen again.

Hey, it could still be the AFM, deciding to work now and again, so I would be grateful to have a spare to test with for when the fault appears again, thank you for that offer, I will forward my address and a payment to cover postage, thanks!

EDIT: (note: your PM inbox is full George!)

RANT TIME..

I HATE TAKING MY CARS TO GARAGES FOR WORK..

My 951 has lovely Linen leather seats, they are perfectly preserved, lovely and bright clean and near white. The white carpets are pristine, sidewalls of the footwells too, lovely and clean. WTF is wrong with some people? They see a stunning classic car with a beautifully preserved clean light coloured interior and still they clamber in with big dirty boots and filthy overalls and dirty oily hands. I just don't get it. Yes, they put a seat cover and floor mat down..but not until after the horse had bolted. It has taken me over an hour this evening with harsh cleaning products to get it clean again and its still not as it was. I am really fed up with filthy mechanics climbing about my car- yes they were in the back too, battery was flat so they have been in the boot so the seat backs and rear carpets have had it too.. that bloody used to climbing in and out filthy Golf's and Vectra's with dark interiors all day they don't think twice. no respect..or rather...too dumb or just plain jealousy.. one of the three, maybe all three. RANT OVER..

Black Beauty · Sep 26, 2014

ORIGINAL: pengers

I had a long term cut-out problem with my '89 turbo.

I completely sympathise as it removes all confidence in reliability.

And any enjoyment. And it's v v difficult to demonstrate to a mechanic as it will undoubtedly run perfect on inspection.

Anyway, mine was crank shaft position sensor manifested in cut-out periods that lasted 5mins to 7hrs and eventually poor running on every start until warm.

I second this.

I had the same problem, use the clarks garage guide to check for correct voltages etc

S

George Elliott · Sep 26, 2014

(note: your PM inbox is full George!)

had a clear out - try again.

perhaps its not the cause - but you are welcome to the afm, re postage, make a charity donation

In just over 20 years of 944 turbos, I have had both the afm issue x2 and the crank sensor issue. once sorted, confidence returns quickly [

]

George
944t